At Diddy Trial, Kid Cudi Says He Was Played by Cassie

Kid Cudi says Cassie played him like a fiddle during their 2011 fling.

The "Pursuit of Happiness" rapper testified Thursday in Diddy's federal criminal trial in NYC, and he talked a lot about his brief relationship with Cassie.

Cudi admitted he felt like he was played by Cassie when she told him things were over with Diddy ... only for her to get back with Diddy after they broke up.

Diddy defense attorney Brian Steel asked Cudi, "She played you?" Cudi said, "Yes." Steel followed up, "You had no clue" that Cassie was back with Diddy? Cudi responded, "No clue."

Kid Cudi told jurors he dated Cassie for less than a month and they broke up because of safety concerns and drama ... he testified Diddy broke into his home upon finding out he was seeing Cassie, and he also said he "knew Sean Combs was violent."

Cudi also testified his Porsche was torched by a Molotov cocktail a couple weeks after things ended with Cassie, and he was convinced Diddy had something to do with it ... and he says when he confronted Diddy about it, Cassie came into the room and that's when he found out they were back together.

Steel asked Kid Cudi if Cassie "was living two different lives," and Cudi said "Yes" ... and Steel asked if both Cudi and Diddy got played by Cassie and Cudi responded, "True."